UCSF-led team discovers cause of rare disease

A large, international team of researchers led by scientists at the University of California, San Francisco has identified the gene that causes a rare childhood neurological disorder called PKD/IC, or "paroxysmal kinesigenic dyskinesia with infantile convulsions," a cause of epilepsy in babies and movement disorders in older children.

The study involved clinics in cities as far flung as Tokyo, New York, London and Istanbul and may improve the ability of doctors to diagnose PKD/IC, and it may shed light on other movement disorders, like Parkinson's disease.

The culprit behind the disease turns out to be a mysterious gene found in the brain called PRRT2. Nobody knows what this gene does, and it bears little resemblance to anything else in the human genome.

"This is both exciting and a little bit scary," said Louis Ptacek, MD, who led the research. Ptacek is the John C. Coleman Distinguished Professor of Neurology at UCSF and a Howard Hughes Medical Institute Investigator.

Discovering the gene that causes PKD/IC will help researchers understand how the disease works. It gives doctors a potential new way of definitively diagnosing the disease by looking for genetic mutations in the gene. The work may also shed light on other conditions that are characterized by movement disorders, including possibly Parkinson's disease.

"Understanding the underlying biology of this disease is absolutely going to help us understand movement disorders in general," Ptacek said.

What is familial paroxysmal kinesigenic dyskinesia?

Familial paroxysmal kinesigenic dyskinesia is a disorder characterized by episodes of abnormal movement that range from mild to severe. Paroxysmal indicates that the abnormal movements come and go over time. Kinesigenic means that episodes are triggered by movement. Dyskinesia refers to involuntary movement of the body.

People with familial paroxysmal kinesigenic dyskinesia experience episodes of irregular jerking or shaking movements that are induced by sudden motion, such as standing up quickly or being startled. An episode may involve slow, prolonged muscle contractions (dystonia); small, fast, "dance-like" motions (chorea); writhing movements of the limbs (athetosis); or, rarely, flailing movements of the limbs (ballismus). Familial paroxysmal kinesigenic dyskinesia may affect one or both sides of the body. The type of abnormal movement varies among affected individuals, even among members of the same family. In many people with familial paroxysmal kinesigenic dyskinesia, a pattern of symptoms called an aura immediately precedes the episode. The aura is often described as a crawling or tingling sensation in the affected body part. Individuals with this condition do not lose consciousness during an episode and do not experience any symptoms between episodes.